This application is related to U.S. Pat. Nos. 5,289,692, 5,477,701, 5,522,231 and 5,877,486, the entire disclosures of which are fully incorporated herein by reference. The above patents are referred to herein collectively as the Low Side patents.
The invention relates generally to heat transfer and refrigeration control systems. More particularly, the invention relates to apparatus and methods for detecting low charge and very low charge conditions of the working fluid in such systems.
The basic building blocks of all refrigeration and heat transfer systems are well known and include a compressor, a condenser, an expansion means and an evaporator, all of which are connected in a fluid circuit having a working fluid such as halogen containing working fluids such as chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), and hydrofluorocarbons (HFCs), and so forth. In an automotive or truck air conditioning system, for example, the working fluid or refrigerant is typically in heat exchange with the vehicle compartment ambient air by means of the evaporator. The liquid refrigerant turns to gas as it passes through the evaporator or endothermic heat exchanger thus absorbing heat from the ambient air. The working fluid leaving the evaporator, preferably is in an all gaseous state, and is drawn into the compressor through a suction line. The compressor increases the gas pressure and the gas then passes through the condenser or exothermic heat exchanger where it is cooled back to a liquid state but is still under high pressure. The liquid high pressure working fluid is then passed through the expansion means, such as an expansion valve, wherein the fluid pressure is adiabatically decreased prior to re-entering the evaporator.
In such systems and others, it is important to detect quickly a low charge or very low charge condition. If the working fluid is being lost, the system will not operate properly and system components such as the compressor can be damaged by operation without adequate lubrication.
Accordingly, the objectives exist for economical, reliable and accurate apparatus and methods for detecting low charge and very low charge conditions of a working fluid in a heat transfer system.
The present invention contemplates apparatus and methods for detecting low charge and very low charge conditions of a working fluid for a heat transfer system. In one embodiment of the invention, such apparatus for detecting low charge of a working fluid in a heat transfer system of the type having a fluid circuit comprising a compressor for pressurizing working fluid received from an evaporator, a condenser and condenser fan for cooling the working fluid received from the compressor, and an expansion device for controlling flow of the working fluid between the condenser and the evaporator, the apparatus comprising: a working fluid state sensor operative in response to a control signal and disposed in the fluid circuit on the outlet side of the evaporator to produce a working fluid state signal; and control means for providing said control signal to the sensor and for controlling operation of the heat transfer system based on a comparison of said working fluid state signal with a predetermined state set point; said control means detecting a low charge condition of the working fluid when the state signal indicates the working fluid superheat exceeds a first predetermined threshold over a predetermined time with the expansion device in a fully open condition.
The invention further contemplates the methods associated with the use of such apparatus, as well as in another embodiment, a method for detecting low charge condition of a working fluid in a heat transfer system of the type having a fluid circuit comprising a compressor for pressurizing a working fluid received from an evaporator, a condenser and condenser fan for cooling the working fluid received from the compressor, and an expansion device for controlling flow of the working fluid between the condenser and the evaporator, the method comprising the steps of:
a) detecting superheat state of the working fluid on the outlet side of the evaporator over a first predetermined time whenever the expansion device is fully open; and
b) detecting low charge condition of the working fluid when the working fluid superheat exceeds a first predetermined threshold over the first predetermined time with the expansion device in a fully open condition.
These and other aspects and advantages of the present invention will be readily understood and appreciated by those skilled in the art from the following detailed description of the preferred embodiments with the best mode contemplated for practicing the invention in view of the accompanying drawings.